FIG. 1 illustrates a physiological monitoring system 100 having a physiological monitor 120, a noninvasive sensor 130 attached to a tissue site 1, and a sensor cable 140 interconnecting the monitor 120 and the sensor 130. Physiological monitoring systems for measuring constituents of circulating blood have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios. The noninvasive sensor 130 has light emitting diodes (LEDs) and a detector. The LEDs transmit optical radiation into the tissue site 1, and the detector responds to the intensity of the optical radiation after absorption by pulsatile blood flow within the tissue site. Based upon this response, the physiological monitor 120 determines measurements for physiological parameters. The physiological monitoring system 100 may incorporate pulse oximetry, which is a widely accepted noninvasive procedure for measuring physiological parameters, such as oxygen saturation and pulse rate among others. The physiological monitoring system 100 may also incorporate advanced features, such as a multiple wavelength sensor and advanced processes for determining other physiological parameters, such as carboxyhemoglobin, methemoglobin and total hemoglobin, as a few examples. The physiological monitor 120 displays the physiological parameters and typically provides visual and audible alarm mechanisms that alert a caregiver when these parameters are outside of predetermined limits.
Pulse oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,650,917, 6,157,850, 6,002,952, 5,769,785, and 5,758,644; low noise pulse oximetry sensors are disclosed in at least U.S. Pat. Nos. 6,088,607 and 5,782,757; all of which are assigned to Masimo Corporation, Irvine, Calif. (“Masimo”) and are incorporated by reference herein.
Physiological monitors and corresponding multiple wavelength optical sensors are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006 and entitled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208, filed Mar. 1, 2006 and entitled Noninvasive Multi-Parameter Patient Monitor, both assigned to Masimo Laboratories, Irvine, Calif. (Masimo Labs) and both incorporated by reference herein.
Further, physiological monitoring systems that include low noise optical sensors and pulse oximetry monitors, such as any of LNOP® adhesive or reusable sensors, SofTouch™ sensors, Hi-Fi Trauma™ or Blue™ sensors; and any of Radical®, SatShare™, Rad-9™, Rad-5™, Rad-5v™ or PPO+™ Masimo SET® pulse oximeters, are all available from Masimo. Physiological monitoring systems including multiple wavelength sensors and corresponding noninvasive blood parameter monitors, such as Rainbow™ adhesive and reusable sensors and RAD-57™ and Radical-7™ monitors for measuring SpO2, pulse rate, perfusion index, signal quality, HbCO and HbMet among other parameters are also available from Masimo.
FIG. 2 illustrates the standard plethysmograph waveform 200, which can be derived from a pulse oximetry system, as described above. The plethysmograph waveform 200 illustrates light absorption at the tissue site, shown along the y-axis 10, versus time, shown along the x-axis 20. The total absorption includes components of static absorption 210 and variable absorption 220. Static absorption 210 is due to tissue, venous blood and a base volume of arterial blood. Variable absorption 220 is due to the pulse-added volume of arterial blood. That is, the plethysmograph waveform 200 is a visualization of the tissue site arterial blood volume change over time, and is a function of heart stroke volume, pressure gradient, arterial elasticity and peripheral resistance. The ideal waveform pulse 230 displays a broad peripheral flow curve, with a short, steep inflow phase 232 followed by a 3 to 4 times longer outflow phase 234. The inflow phase 232 is the result of tissue distention by the rapid blood volume inflow during ventricular systole. During the outflow phase 234, blood flow continues into the vascular bed during diastole. The plethysmograph baseline 240 indicates the minimum basal tissue perfusion.